Try this test: String up the guitar with an .008 (high E); then an 009. (as "b" string); a .010 ("g"), a .011 ("d"); an .012 (for a "d") an .013 ( for the"a"), and an .014 (low "e"). Now...tune them all to the same pitch (high "e"). Then compare. As a control, reverse the placement ( starting with the .008 on the low "e" side), to eliminate body resonance factor. Do the same with the thicker strings (.052/.049/.046/.042/.040/.038) and repeat the test. The difference that you hear (if any) is the answer.
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user7012Sep 7 '13 at 0:59

4 Answers
4

All else being equal, increasing the string gauge will improve the sound quality and reduce the playability. The sound quality will improve due to the added tension (necessary to bring the thicker strings up to pitch). On the other hand, the added tension will typically increase the bow of the neck, raising the action and reducing the playability.

Switching gauges often requires a truss rod adjustment. With the set-up optimized for a specific gauge, the truss rod may still require seasonal tweaks (for humidity changes). A discussion of guitar set-up, however, is beyond the scope of this answer.

I did not downvote, but it is not an established truth that increasing string gauge increases the sound quality. Some people think thinner is better in terms of both playability and sound. I'm not one of those, but that is one reason for downvoting the answer.
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Meaningful UsernameJun 17 '14 at 20:46

The concept of Quality drove Phaedrus insane; I will not attempt to define it here.
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Kirk AJun 18 '14 at 11:22

Bear in mind that if you use thicker strings on some guitars with thin necks (especially electric), the extra tension required can pull/bow the neck a little, making the action higher about halfway down the neck. Effectively it's like an archery bow, just much straighter.

Also it can affect a whammy bar (tremolo arm) if you have one. Eg on a Fender strat, it can pull the bar upwards a fraction, thus affecting intonation and making it more difficult to tune.

So if your guitar has think strings lik .008 or .009 and you put a set of .012 on, you may find other affects as above make it a bit awful unless you have the guitar set up to take them (I have had this happen)

What effect does my choice of string gauge have on the sound of my guitar?

What effect does it have on playability?

Well, this depends on what your guitar is.

With acoustic guitars, the strings move the top of the guitar, creating the sound to be projected, so those who need more volume went with bigger guitars with bigger strings, with higher action so the strings will ring out. On a purely unadulterated flat-top acoustic guitar, this is the secret to getting volume. That's the main effect on your sound: louder. More easily heard above the rest of the mess. And heavier strings with higher action will put a greater gap between string and the fretboard, making you work harder to get it to do anything at all, so it messes up your playability. If you're looking for more playable and not needing quite the volume, or can make it up with amplification, you don't need the boost big strings get you and you can lighten up, and so can the maker. There are things put into Martin dreads just so that they can survive being attacked by bluegrass pickers.

The same inverse relationship between string size and playability exists on electric, but because you don't really need the strings for volume -- you have an amp and pedals for that. There is an element of it; if you have a guitar and a set of settings for the same gear, you'll have less volume, but there should be something you can turn up to compensate.

A thicker string won't sound as bright. Play something on the high E and compare five frets up on the B string, then another four on the G string, and you'll hear that difference. Of course, you have tone controls to modify that should your string not give you what you want.

For a while, I took the increased tension as an enforcer of self-control. I can't bend out of tune if I can't bend beyond a full step, or if I have to work hard to fret the note in the first place. I'm largely beyond that, and when I experimentally put .008s on my Tele, I thought it was perfect, that I had an effortless instrument to play.

The thicker the string, the more tension it needs, to produce the same note.

Sound

Thicker, tighter strings, have a more "focussed" sound. They reach their resonant frequency more quickly, because the extra tension leaves them less scope to flap around.

Thicker, tighter strings, plucked the same distance, are louder, because they contain more energy. There is more metal being waved back and forth in front of the pickup. There is more kinetic energy to be transmitted to the sounding board.

Looking at this in the opposite direction, heavier strings need to vibrate less in order to produce the same volume as a narrower string. So you are less likely to experience fret buzz at the same loudness.

Thicker, tighter strings, plucked the same distance, have more sustain, because they contain more energy and it takes longer to disperse.

Of course, that energy doesn't come from nowhere. It takes more strength to pluck a thicker string.

Playability

The more tense a string is, the harder it is to fret -- you have to press harder. Beginners are likely to prefer narrower gauges and looser strings, until they develop callouses on their fingers.

Players wishing to play very fast solos often choose light strings, because they can make gentle, fast fretting movements.

The looser a string is, the easier it is to bend. This is an advantage if you want to incorporate dramatic bends into your playing. However, with very light strings, it can be too easy to bend notes -- to the extent that a beginner can have trouble playing a chord in tune, accidentally bending one string or another.

Typical gauges

Strings are sold individually, but most people buy sets. Buying a set gives you the confidence that the gauges work well together. As shorthand, the gauge of the top E string is used to describe the set. For example "a set of 10s" would refer to a set in which the top E string is 0.010 inches.

On both electric and acoustic metal-strung guitars:

0.009 sets are considered very light

0.014 sets are considered very heavy

Correspondingly, the bottom E strings tend to range from 0.047 to 0.059.

The choice of which gauge to use is a personal one, based on your playing style and the tone you are trying to achieve.

So, what's the the advantage/disadvantage if someone pick a thick string for plucking, and s/he likes when the string is loose, cause its easier to have a better control over them? (that's me)
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iamcreasyNov 16 '11 at 15:31

Actually since it sounds like you are very much a beginner, I would recommend you play with 10s. They're not too easy to bend, and they are easy to fret. Change later, if you decide you want a different sound.
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slimNov 16 '11 at 15:40

So, there is no problem if I loosen a thick string? I never knew what's thick string was for, except the extra base it causes.
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iamcreasyNov 16 '11 at 15:41

1

I don't really understand what you're asking. If you loosen any string, it will play at a lower pitch. The strings are the thicknesses they are so that when they are all at about the same tension, they have the desired pitches.
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slimNov 16 '11 at 15:47